Emphasis on Learning Empowers the Laboratory’s Lasers

THE National Ignition Facility (NIF), a laser the size of three football fields, creates conditions more extreme than those present at the center of the Sun. To build the largest and most energetic laser in world, capable of operating within precise microscopic realms and billionths-of-a-second timescales, required a remarkable series of achievements in design and engineering. NIF continues to grow in capability to support the National Nuclear Security Administration’s (NNSA’s) Stockpile Stewardship Program (SSP), the Discovery Science Program, and other national security applications.

Drawing on decades of high-energy and high-power laser innovation, Lawrence Livermore commissioned the petawatt-class Advanced Radiographic Capability (ARC) laser in December 2015 for the NNSA as an important counterpart to NIF. As described in the feature article, Two World-Class Lasers Combine to Power Applications, to become the most energetic short-pulse laser in the world, ARC was not only built on the shoulders of NIF, but was also constructed by sharing components at the heart of NIF. In short, ARC is a very big laser inside the biggest laser of all.

As with NIF, the complexity and sheer magnitude of ARC’s energy and power output required much more than a flip of the switch before becoming not merely operational but efficient for its users. NIF operates 24 hours a day, 7 days a week, with a shot rate of more than 400 shots per year because the NIF team never stopped learning or raising the bar. The NIF team had to work hard to perform enough commissioning shots on ARC without disturbing the schedule for all the other NIF deliverables. Now, as the number of ARC shots begins to ramp up, we will see exciting results achieved by ARC applications. We expect ARC to continue to advance and deliver new insights and understanding vital to helping fulfill the Laboratory’s missions.

We want to continue improving the quality of the implosions in NIF experiments so that less energy and power are required to achieve ignition. At the same time, we are exploring ways to increase the laser’s energy and power. In March of this year, a shot achieved a record-breaking energy of 2.1 megajoules, which was 15 percent higher than NIF’s design specifications.

For its part, ARC specifically addresses the effort to improve the quality of NIF implosions. Developed first and foremost for SSP, ARC will enable us to look at implosions late in time and see what is happening at the final and most critical stages of compression. Only ARC can generate x rays strong enough to produce radiographs on NIF that reveal this information. High-energy backlighting and Compton radiography backlighting are two promising applications of ARC that will let us see more detail than ever before. This learning will continue growing our understanding of what is required to achieve ignition on NIF.

Every program that wants to remain on the forefront of science and technology must frequently infuse new ideas. By also using ARC for Discovery Science experiments investigating fundamental physics, such as proton acceleration and matter–antimatter pair creation, we broaden our expertise in experimental high-energy-density science, our innovations in diagnostics and target platforms, and our insights into the nature of the universe. Time and time again, Discovery Science platforms, diagnostics, and other capabilities have carried over to advancements in SSP.

To advance our laser design and engineering acumen, we continue to develop major new laser capabilities such as ARC.
We have also built on our experience with ARC to develop another world-class laser. In June, the Laboratory commissioned the innovative High-Repetition-Rate Advanced Petawatt Laser System (HAPLS) at the Extreme Light Infrastructure Beamlines facility in the Czech Republic. (See S&TR, July/August 2017, Advanced Laser Promises Exciting Applications.) Taking only three years to design, build, and meet its performance goals, HAPLS pushes the limits of high-repetition-rate, high-average-power petawatt lasers, and again shows that Lawrence Livermore continues to be a world leader in innovative lasers.

As we learn, we want to challenge ourselves to embrace opportunities to learn even more—just what we are doing by developing world-leading technologies such as ARC. Stewardship of NIF means growing the next generation of science, engineering, and operations talent by constantly challenging these men and women to solve hard problems, so they are always ready to support the incredibly important missions with which the Laboratory has been entrusted.